Historically, repair of dynamic random access memory (DRAM) arrays is achieved by replacing defective word-lines or bit-lines with redundant word-lines or bit-lines, using a laser to open circuit fuses made of a conductive material. As devices continue to shrink, the relative size of these laser fuses is limited by the wavelength of the laser employed. Therefore, the size of the laser fuse cannot be shrunk indefinitely. Thus, such ablative laser-blown fuses become more difficult to implement due to the excessive silicon space required to avoid damage to neighboring circuits. Further, repairing an integrated circuit chip by open circuiting thousands of laser programmable fuses is a time consuming process.
An alternative fuse approach is to implement an electrically programmable fuse. One-time electrically programmable fuses, referred to as e-fuses, have become popular due to circuit and system design flexibility which they provide. For example, an e-fuse can be programmed even after the integrated circuit chip has been packaged and installed in the system (unlike the laser fuse approach). For instance, a customer can tailor a circuit design to the specific needs of the application after the circuit is installed in the field. An e-fuse also provides freedom to alter a circuit design, or fix a problem that may occur during the life of the product. Electrically programmable fuses are much smaller than ablative-type fuses, resulting in circuit density advantages. Although electrically programmable e-fuses provide these noted benefits, integration with standard CMOS processing has been problematic. Furthermore, obtaining a tight distribution of open circuiting voltages derived using today's normal operating voltages continues to be challenging. Existing e-fuses typically require voltages in excess of normal supply voltages for programming. As operating voltages continue to be aggressively scaled down with each succeeding generation of integrated circuit technology, obtaining sufficiently high voltages for programming an e-fuse can tax the electrical operating limits of the technology, and increase circuit complexity, for example, due to the need for charge pumps.
In view of this, there remains a need in the art for enhanced electrically programmable fuses, and methods of fabrication thereof, which may be readily programmed with today's on-chip operating voltages, and be readily integrated with standard semiconductor circuit fabrication processing.